FIG. 1 schematically illustrates an electronic device comprising an integrated circuit 100, and a device 110 for protecting integrated circuit 100 against electrostatic discharges.
Integrated circuit 100 comprises terminals of connection to external devices. More particularly, in the shown example, integrated circuit 100 comprises a terminal 101 of application of a high power supply potential VDD of the circuit, a terminal 102 of application of a low power supply potential or reference potential GND of the circuit, and an input/output terminal 103 (10) of the circuit, capable of supplying and/or of receiving data signals.
Protection device 110 is coupled to connection terminals 101, 102, and 103 of integrated circuit 100. The function of protection device 110 is to enable, when an electrostatic discharge occurs on one of the connection terminals of integrated circuit 100, a fast removal of the discharge, to avoid for the latter to damage circuit 100.
Protection device 110 of FIG. 1 comprises two diodes 111 and 112, series-connected between power supply terminals 102 and 101 of integrated circuit 100. The junction of diodes 111 and 112 is coupled to input/output terminal 103 of circuit 100. More particularly, in this example, diode 111 has its anode connected to low power supply terminal 102 and has its cathode connected to input/output terminal 103, and diode 112 has its anode connected to input/output terminal 103 and its cathode connected to high power supply terminal 101. Protection device 110 further comprises a Zener diode 113 connected in parallel with diodes 111 and 112, between the low and high power supply terminals 102 and 101 of circuit 100. Zener diode 113 has its anode connected to terminal 102 and its cathode connected to terminal 101.
Protection device 110 operates as follows. When a overvoltage which is positive with respect to the reference potential or ground potential GND occurs on terminal 103 of integrated circuit 100, this overvoltage is removed via diode 112, which is then forward-conductive, and via Zener diode 113, which then conducts in avalanche. When an overvoltage which is negative with respect to reference potential GND occurs on terminal 103 of circuit 100, this overvoltage is removed via diode 111, which is then forward-conductive. When an overvoltage which is positive with respect to reference potential GND occurs on terminal 101 of circuit 100, this overvoltage is removed via Zener diode 113, which then conducts in avalanche. When an overvoltage which is negative with respect to reference potential GND occurs on terminal 101 of circuit 100, this overvoltage is removed via Zener diode 113, which is then forward-conductive.
For positive overvoltages, the threshold for triggering the protection is set by the avalanche threshold of Zener diode 113. The triggering threshold should be selected to be greater than power supply voltage VDD of integrated circuit 100, and greater than the maximum voltage level of the data signals capable of transiting on input/output terminal 103 of circuit 100, but smaller than the maximum overvoltage level capable of being withstood by circuit 100 with no degradation.
In recent integrated circuit manufacturing processes, the window within which the protection device triggering threshold should be selected is relatively limited, which poses problems on the design of the electronic systems. In particular, for each component to be protected, a specific protection device should be selected, by taking into account the levels of the nominal operating voltages of the component, and the maximum overvoltage level that the component can withstand.
To ease the design of electronic systems and decrease costs, it would be desirable to have an electrostatic discharge protection device with an adjustable triggering threshold, to be able to use a same protection device in systems having different nominal operating voltages.